1. Field of the Invention
The invention relates to an abnormality detecting device for detecting an abnormality in a hydrogen discharge valve provided in a fuel cell system.
2. Description of the Related Art
In a fuel cell system in which electric power is generated by supplying fuel gas and oxidizing gas to a fuel cell stack constituted by stacking plural cells in series, there is a known structure in which unreacted hydrogen gas is reused for a cell reaction by making hydrogen off-gas (anode off-gas) discharged from an anode gas channel flow back to an anode. A hydrogen discharge valve for discharging part of the hydrogen off-gas is provided in a hydrogen off-gas circulation passage. By regularly opening the hydrogen discharge valve when a concentration of ingredients other than hydrogen contained in hydrogen off-gas becomes high, a concentration of hydrogen to be supplied to the anode is maintained appropriately. However, if an abnormality occurs in the hydrogen discharge valve and opening/closing operation of the valve cannot be performed properly, a problem occurs in a cell operation. Accordingly, Japanese Patent Laid-Open Publication No. 2003-92125 discloses a technology for detecting a hydrogen discharge command to a hydrogen discharge valve, and determining whether a failure has occurred in the hydrogen discharge valve based on a target pressure of a fuel supply portion of a fuel cell stack and an actually detected value.
According to the technology disclosed in this publication, however, the determination as to whether a failure has occurred in the hydrogen discharge valve is made only when the fuel cell is being operated normally. Accordingly, when the fuel cell is in a transition state, for example, when an accelerator pedal is depressed abruptly, an appropriate failure determination cannot be made.
Document U.S. Pat. No. 5,441,821 discloses an electric power generation system having a regulated vacuum ejector for recirculating the fluid fuel stream. The system includes a fuel cell stack, a pressurised fuel supply having a pressure control valve for regulating the pressure of the fuel supply, a vacuum ejector interposed between the fuel supply and the stack fuel stream inlet, a pressure transducer interposed between the ejector discharge outlet and the stack fuel stream inlet, and a pressurised oxidant supply with a pressure transducer. The ejector suction inlet is fluidly connected to the fuel stream outlet of the fuel cell stack. The fuel stream pressure transducer transmits a signal to the pressure control value to adjust the pressure of the fuel supply when detected pressure of the fuel stream deviates from a predetermined value. The oxidant stream pressure transducer transmits a signal to the pressure control value to adjust the pressure of the fuel supply when the detected pressure of the oxidant stream changes.
Further, document JP 09-209810 discloses a failure detector for intake air control valve mechanism of an engine to easily detect a failure condition of an intake air control valve mechanism without accompanying complexation of construction and control, and to externally display the failure condition rapidly and certainly, by composing a driving means control part and a failure judging part in an ECU, and externally displaying the failure condition of the intake air control valve mechanism on an display. In this detector, an engine operating condition detecting means is arranged which judges whether or not an engine operating condition is in regular condition. Further, a pressure sensor detects pressure in an intake air pass when the intake control valve is opened/closed. When pressure difference in opening/closing periods between the detected pressure is at a predetermined value or more, failure judging means in the ECU judges that the engine operating condition is normal, and when pressure difference is smaller than the predetermined value, it judges that the engine operating condition is normal, and when pressure difference is smaller than the predetermine value, it judges that the engine operating conditions is in failure condition. Displaying means externally displays whether or not the engine operating condition is in failure condition on the basis of these judgement.
A fuel cell system form an underwater vehicle is further disclosed in documents U.S. Pat. No. 3,748,180. This fuel cell system has at least one fuel cell module for supplying electrical power for said vehicle. A first tank containing hydrogen is connected to one reactant chamber of a fuel cell module and second tank containing oxygen is connected to another reactant chamber of the fuel cell module. The hydrogen product water output from the hydrogen reactant chamber is condensed and separated and the water produced is stored in the first tank containing hydrogen. The fuel cell module is placed in a containment vessel which is pressurised with nitrogen. A catalytic reactor is provided in the containment vessel to form water in the event that there are simultaneous leaks in both the hydrogen and oxygen high pressure supply lines. A pressure transducer is also provided in the containment vessel for shutting down the system if there is a high pressure leak in either the hydrogen or oxygen line.
Further, document EP 1 223 631 A2 discloses a method and apparatus for detecting leakage current in the coolant of a fuel cell stack between said stack and the ground stack chassis, using a voltmeter to measure the voltage across the coolant. If the coolant voltage is at or below a predetermined level, an excessive level of conductivity in the coolant exists, and the presence of leakage current is reported.
Further, document US 2003/077487 A1 discloses methods for improving the cold starting capability of an electrochemical fuel cell wherein temperature dependant methods can be used to improve the cold start capability of fuel cell electric power generation systems. A method of ceasing operation of an electric power generation system improves the cold start capability and freeze tolerance of a fuel cell stack by reducing the amount of water remaining within the passages of the stack. The method involves purging one or more of the fuel cell stack oxidant and fuel passages at shutdown prior to allowing the fuel cell stack to drop to temperatures below the freezing point of water. Preferably purging at shutdown is conducted at a temperature below the stack operating temperature. Another method, used at start-up, involves directing a coolant fluid stream to the fuel cell stack only after a predetermined temperature above the freezing temperature of water is exceeded. Preferably, after freezing the fuel cell stack is heated to a temperature above its normal operating temperature before the operation is commenced.
It is therefore an object of the invention to solve the above-mentioned problem, and provide an abnormality detecting device for detecting an abnormality in a hydrogen discharge valve regardless of an operation state of a fuel cell.